Human skin consists of epidermis and dermis, besides the outermost layer thereof (keratin); and hypodermis containing adipose tissues resides thereunder. The epidermis consists mainly of keratinocytes; and the dermis consists mainly of dermal fibroblasts.
Functional cosmetic materials targeting for ameliorating wrinkle and inhibiting skin aging are mainly natural products, chemical compounds and peptides for facilitating the expression of collagen proteins in the dermal fibroblasts (major cells of the dermis) or inhibiting the proteases against collagen proteins; in addition to proteins such as growth factors, cytokines and the like, for facilitating the growth of dermal cells. However, it is well known in the art that it is very difficult for most active materials having such effects to pass through the epidermis of the skin and reach the dermis.
The epidermis acts as a barrier for preventing the permeation of external harmful substances, ultraviolet, chemical substances, and so on and maintaining the moisturization in the skin. The major cell functioning as such is keratinocytes and it is known in the art that keratinocytes regulate immune responses in the sub-dermal tissues by secreting inflammatory regulators (cytokines, chemokines, etc.), along with maintaining the skin barrier. It is known in the art that such a skin barrier function of the epidermis is originated from the bindings between keratinocytes, i.e., the expression and activation of cell-to-cell junction proteins. The junction proteins function as an important barrier not only for providing a primary physical defense from external infections, but also for protecting dermal cells and inhibiting immune imbalance from chemical stimulations inside or outside the cells. The junction proteins are usually divided into four groups: tight junction proteins, adherence junction proteins, gap junction proteins, and desmosomes. Among them, tight junction proteins (e.g., claudins, occludins, ZO-1, 2, etc.) are known as a major factor contributing to the cell barrier protection, by preventing the migration of molecules, especially water-soluble materials, through the space between cells; and inhibiting cell permeability. Therefore, it is expected that a material capable of facilitating the bindings between keratinocytes and/or increasing the expressions of junction proteins may be useful for inhibiting a skin-aging or a skin-wrinkle formation, through protection and activation of the skin barrier.